Electron-emitting element



Dec. 18, 1928. 1,695,899-

L. M cuLLocH ELECTRON ,EMl-TTING ELEMENT Filed Sept. 27. 1922 INVENTOR Leon flcculloqh ATTORNEY WITNESSES:

Patented Dec. 18, 1928.

UNITED STATES PATENT orrlclz.

LEON MCCULLOCH, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, -A CORPORATION OF PENNSYLVANIA.

ELECTRON-EMITTING ELEMENT.

Application filed September 2?, 1922. Serial No. 590,777.

My invention relates to thermionic devices and particularly to electron-emitting elements and processes of manufacture thereof.

The principal object of my invention is to provide an improved method of coating electron-emitting elements, whereby coated Wehnelt elements may be obtained having highly desirable characteristics and whereby material economies may be efiected 1n the time required for the coating process.

In the ordinary methods of manufacturing filaments of the class described, coated filaments have been produced, the coatings of which were of variable thickness, rough and poorly adherent. Another disadvantage of the coated filaments of the prlor art resides in the fact that most or all of them must be stored in sealed containers, inasmuch as the chemical composition of the same is subject to change in the presence of water vapor and of carbon dioxide.

According to my invention, I provide a method of coating filaments which produces a filament coating having the desired characteristics. Briefly, the process consists in applying to a conducting element successive coatings of an aqueous solution of barium and strontium nitrates. Each successive coating is heated to ignition temperatures in an atmosphere of carbon dioxide to cause the nitrates of barium and strontium to be converted into carbonates.

The necessary heating to form the carbonate coating from the nitrate coating may be done either b passing the filament through a furnace lled with carbon dioxide or by heating the filament with electrical energy in a carbon-dioxide atmosphere. Both methods have been used withsuccess. The resulting coated filament is of such definite and unchanging composition as to withstand all necessary handlings and may be kept indefinitely in an atmosphere of air or carbon dioxide.

The final step in the treatment of the filament occurs when the filament has been mounted in a vacuum tube as the cathode element thereof, the carbonates being in whole or in part reduced to oxides when the tube is subjected to the usual hardening process.

With

these and other objects in view, my

invention further consists in the o erations and products hereinafter descri ed and claimed and illustrated in the accompanying drawings, wherein I The single figure is a view partially diagrammatic and partially structural, showing one form of apparatus for carrying my process into effect, together with the necessary electrical circuits. In order to illustrate the method embodymg my invention, I have shown an arrangement of apparatus which has been found,

in practice, well adapted for carrying my nvention into effect. Briefly, the apparatus includes one or more vertically positioned tubes, as 1 and 2, forming chambers 3 and 4, respectively, the lower portions thereof terminating in a common tubular member 5. The tube 5 is carried by a removable stopper member 6 of a receptacle 7 and extends below the surface of a coating solution 8 contained therein, thus forming an air-tight space 9 above the surface of the coating solution 8.

The solution just mentioned may consist of an aqueous solution of barium and strontium nitrates. In practice, I have found that such solution-is preferably obtained by dissolving a mixture containing three parts of barium nitrate and two parts of strontium nitrate in water in the ratio of five parts of the mixture to one hundred parts of water. While I have specifically mentioned nitrates of barium and strontium, other salts may be successfully employed, such, for example, as bromides and iodides of metals producing electronically-active oxides, and'also salts formed by the union of such metals with organic acids.

The upper ends of the tubes 1 and 2 are fitted with removable stopper members 11 and12, carrying supporting structures 13 andl l, which extend down into the tubular members -1 and 2, respectively. The structures 13 and 1 1 may carry filaments 18 and 18, respectively, which are to be coated.

The supporting structures 13 and 14 may be provided with external circuit terminals 15, 16'and 17, 18, respectively, which serve to connect the several filaments in seriescircuit relation to an external energy source 19 through an adjustable resistor 21 and a switch 22. In practice, a 220-volt alternat- We seem: 1y excite the several filam nts. here p ft more fully explainedi I tively, terminate in a common tubularmem ber 27 which is connected, through "a tube 29 and a valve 31,.to 'a common receptacle 28 containing carbon dioxide under pressure. The common 'tubularmember 27 is also connected to an air-valve apparatus 30 designed to receive the gas contained in the tubes 1 and 2, when the latter is forcedout; of the same duringthe coating pr'ocess, all.

as hereinafter explained. v 1

1 The air-valve apparatus 30 comprises a receptacle 32 containing a a. liquid 33, p as water. A second receptacle 34, having a constricted openin 35 at one end provided with a perforate stopper .36 carrying a tubular member 37 and having an enlarged opening 38 at the opposite end, is vertically positioned in the liquid 33 with the tube 37 extending vertically upwards. ,The tube 37 may be maintained in such position by means of a support 39, which is in sliding contact with the tube, to provide for the vertical motion of the receptacle 34 occasioned by variations in the pressure ofthe gascon: tained in the tubes 1 and2, as hereinafter explained.

The level ofthe solution in the tubes 1 and is connected to the high-pressure source, as

just stated, thereby forcing the solution 8 partially out of the receptacle 7 and up into the tubular members 1 and 2 and hence com,- pletely covering the filaments 18 and 18, which are to be coated. In another position of the valve 42, the space 9 is connected to atmosphere through a tubular member 43 constricted at its open end sufiiciently to cause the coating solution to return, by gravity, to its initial position in the chamber 7 at a predetermined slow rate, say two inches per second whereb ro r drain e from the filameritsis pro videdi avg Attention. is directed to the fact that, as the solution rises in the tubular members 1' and 2, the gas or air contained therein is forced out of the same and into a space 44 formed above the surface of the liquid 33..

The variations in the size of this space, re-

A pair of tubular members 23" and-24', which extend from openings' -25 and 26 near the upper ends of the tubes 1. and 2, respecisu1tin" from*the vertical j otion oflthe receptac e,,' are suchjaQ to1 .compen sate for. the

canre'adily-be seen. i In order 'to more fully. complete the disvariations in the pressure of the gas 0on tained in the tubular members land 2, as.

closure of my invention, I: will statethe. method of coatinglthe filament embodying my invention, using: values. which have'been found in practice to produce a filament havistlcs.

first thoroughly cleansed in any known manher, as by heating-thesame to incandescence in the hereinbefore mentioned charactcr-' The filaments "which are to be coated are to' remove accumulated {dirt and dust,.'and-' structures 13' and14i3;

- The two-way-valve'a42 isthenoperatedit cause the coating solution 8 to completely cover and uncover. the filaments-"18 and 18' as preViously-statedQthe rate of the .fall'of,

are then, mounted upon. the supporting" the coatingsolution 8 in the several tubes and 2 being such thatproper drainage from- I the filaments 18and 18' isprovided, Other-.j

wise, an imperfect coatingis obtained:

' While the coating solution is flowing out of;

the tubes land 2, the valve 31 .is'open'ed to fill the tubular members land 2 and theai'r space 44 ofzthe airrvalv'e apparatus .30 w th carbon dioxide. The swltch 22 is then closed to heat the filaments 18 and 18 to ignition temperatures, say .1800 O. The

effect of heating the.filam ents; inthe atmosphere of carbon dioxide isto change the nitrates of barium and-strontium into car-s v bonates. Thus, a coating ofg'barium -and. j strontium carbonates s formed on the fila-iff ments. r. The dipping and heating] of the filaments are Peated unitilfl'a coating qfwsufficientf thickness is built p- -W i1e ithas been" found that a. filament having a e long,

life i's'obtained with only sixcoats, the proc-- ess may be continued until, say,-forty coats are formed in order to provide a filament I having a large factor of safety. The coated filaments may now be removed from the supporting structure and stored in suitable containers.

The final step in theprocess occursiwhen' the coated filament has been embodied in a thermionic device (not shown) as the oathode element thereof and theusual treating process started.

As is customary, during the treat g ent of thermionic'tubes, the several elem'e s contained thereinare heated to high tempera- 'tures inorder to drive out the occluded gases and it 1s durlng such heat treatment that.

the carbonates of barium and "strontium constituting the coating are converted into oxides. g Thus, in my system, the final step 016C011. verting the filament coatings into oxides is lso combined with the usual evacuating process, thereby decreasing the time and expense involved in the manufacture of thermionic desire, therefore, that only such limitations shall be applied thereto as are specifically set forth in the appended claims or demanded by the prior art.

I claim as my invention: 1. The steps ina method of treating a conducting element which consistin coating said element with an aqueous solution of at least one compound of at least one metal of the alkaline-earth group and subsequently heating said element to ignition temperature in an atmosphere of carbon dioxide 2. The steps in a method of treating a conducting element which consist in coating said element with an aqueous solution of nitrates of a plurality of metals of the alkaline-earth group and subsequently heating said element in an atmosphere of carbon dioxide to ignition temperatures.

3. The steps'in. a method of treating a conducting element which consist in coating said element with an aqueous solution of barium and strontium nitrates and subsequently heating said coated element in an atmosphere of carbon dioxide to temperatures high enough to cause said nitrates to change into carbonates.

4. The method of manufacturing a coated filament which consists in depositing thereon successive coatings of an aqueous solution of a compound of a metal of the alkaline-earth group, subjecting each coating to ignition temperatures in an atmosphere of carbon dioxide and finally heating the coated filament in an atmosphere containing little or no carbon dioxide.

5. The method of treating a conducting element which consists in depositing upon said element a coating of an aqueous solution of nitrates of a plurality of metals of the alkaline-earth group, subjecting said coating to ignition tem eratures in an atmosphere of carbon dioxlde and finally heating the coated filament in an oxidizing atmosphere.

6. The process of manufacturing a \Vehnelt-cathode which consistsin depositing upon said cathode successive coatings of an aqueous solution of barium and strontium nitrates, subjecting successive coatings in an atmosphere of carbon dioxide to temperatures high enough to cause the coatings of barium and strontium nitrate to be converted into barium and strontium carbonates and finally heating the cathode in an oxiilizing atmosphere.

. The method of manufacturing an electron-emitting element which consistsin depositin upon said element successive coatmgs of an aqueous solution of barium and strontium compounds, heating the same 1n an atmosphere of carbon dioxide subsequent to each coating to a temperature sufiicient to convert the said compounds of barium and strontium intocarbonates and finally heating said element in an atmosphere containing little or no carbon dioxide to convert the carbonates of barium and strontium into oxides.

8. The process of manufacturin a \Veh nelt-cathode which consists in epositing upon said cathode successive coatings of an aqueous solution of a compound of a .metal of the alkaline-earth group, heating said cathode after each coating to ignition temperatures in an atmosphere of carbon dioxide and subsequently embodying said cathode in an electron tube and subjecting said cathode to ignition temperatures during the hardening process of thetube.

9. The method of manufacturing an electron-emitting element which consists in depositin upon said element successive coat ings 0 an aqueous solution of at least one compound containing a metal or metals of the alkaline-earth group, heating said element after each coating in an atmosphere, of carbon dioxide to such temperatures as to cause the coating to be converted into carbonates and subsequently mounting said element in an electron tube and converting said carbonates into oxides during the treating process of the tube. p

10. The methodof manufacturing and as: sembling the parts of an electron-tube comprising an oxide-coated filament which con sists in preparing and keeping the filament ing of such nature as to be convertible intoa vapor or vapors and a carbonate or carbonates of said metal or metals when heated in an atmosphere of carbon dioxide, and subsequently subjecting said coating to such heating in said atmosphere of carbon dioxide.

12. The method of preparing a filament material which consists in initiallycoating an-element withla-liquid' conta ning a com-- pound of a metal, sa1d liquidbeing of such.

nature as to be convertible into a va or or vapors and a coatln containing a car onate of said metal when eated in an atmos here of carbon dioxide, and subsequently su ject ing said coating to such heating in said ati mosphere of carbon dioxide.

.13. The method of preparing a filament material whichconsists in initially coating an element with a liquid contaimn compounds of a plurality of metals, sai liquid being of such nature as to be convertible into a vapor or vapors and coating containing carbonates of said. metals when heated in an atmosphere of carbon dioxide, and subsequently subjecting said coating to such heating in said atmosphere of carbon dioxide.

14.; The method of making thermionically active electrodes which comprises coating an electrically conductive ha y with the carbonate of an alkaline earth metal and heating said body under conditions unfavorable to the decomposition of the carbonate to cause the alkaline earth carbonate to adhere thereto.

' 15. An'electrode adapted to be-rendered thermionically active comprising an electrically conductive body having a coating of alkaline earth carbonates baked thereon in a firmly adherent manner, said carbonates being capable of conversion to the oxides upon application of heat to the body.

16. A filamentary electrode adapted to'be' rendered thermiomcally active comprisin a metallic core having a .coatingof alkaline earth carbonates, free from organic material, baked thereon"'"in a firmly adherent manner, said carbonates being capable of conversion to the oxides upon theapplication of heat to the filament.

In testimony whereof, I have hereunto I "subscribed my name this 21st day of Septembcr, 1922. Y

LEON MGCULLOCH. 

